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This paper continues analyses on organic compounds for application in neutron dosimetry performed through electron spin resonance (ESR). Here, the authors present the results obtained by ESR measurements of a blend of ammonium tartrate dosemeters and gadolinium oxide (5 % by weight). The choice of low amount of Gd is due to the need of improving neutron sensitivity while not significantly influencing tissue equivalence. A study of the effect of gadolinium presence on tissue equivalence was carried out. The experiments show that the neutron sensitivity is enhanced by more than an order of magnitude even with this small additive content. Monte Carlo simulations on the increment of energy release due to gadolinium presence were carried, and the results were in good agreement with the experimental data.

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Potential electron spin resonance (ESR) dosimetric application of different compounds of sodium tartrate, such as sodium tartrate dihydrate, sodium bitartrate monohydrate and potassium sodium tartrate tetrahydrate, was investigated in the range of 0.74-25 Gy. While the radiation-induced intermediates produced in these compounds are similar, their radiation yields are different. It is found that the radiation yield of sodium tartrate dihydrate is higher than other compounds of sodium tartrates. Comparison of the radiation yields were also made between well-known samples of ammonium tartrate, alanine and lithium formate. It is found that the radiation yields of sodium tartrate dihydrate, sodium bitartrate monohydrate and potassium sodium tartrate tetrahydrate have the values of 1.22, 0.18 and 0.13, respectively.

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While unirradiated potassium tartrate (PT) samples do not exhibit any electron spin resonance signal, irradiated ones contain many resonance signals. A power function of the radiation dose was found to describe well the dose-response curve of the central resonance signal, and adjusting the microwave power and modulation amplitude to be 2 mW and 1 mT, respectively, was found to increase the sensitivity of PT. The radiation sensitivity of PT and the accuracy of the measured radiation dose were found to be G = 0.42 and 6 %, respectively.

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Effects of gamma radiation on solid sodium tartrate dihydrate (NaTA) were studied using electron spin resonance (ESR) spectroscopy. One main singlet located at g = 2.0034 and many weak lines located at low and high magnetic field sides were found in the irradiated samples. Dosimetric and kinetic features of the radical species responsible for the experimental ESR spectra were explored through the variations in the signal intensities with respect to applied microwave power, temperature and storage time. Activation energies of the involved radical species were also determined using data derived from annealing studies.

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The room-temperature and high-temperature kinetic features of the radical species produced in solid dl-tartaric acid (dl-TA) gamma-irradiated at room temperature and the dosimetric potential of this acid were investigated in a detailed ESR study. Irradiated dl-TA presents an ESR spectrum with many unresolved resonance lines even at the lowest radiation dose applied (100 Gy). The evolution of the signal intensities associated with induced radical species with microwave power, applied dose and temperature was followed. Three groups of resonance intensities originating from three different radicals exhibiting different spectroscopic features, stabilities at room and high temperatures, and radiation yields were found to take part in the formation of experimental ESR spectrum. These three species were calculated to exhibit spectroscopic features similar to those already reported for X- or gamma-irradiated deuterated single crystals of dl-TA and assigned as I, II and III. The same radical notation was adopted in the present work, and the intensities related to these species were denoted with the names of their corresponding species. Species III, which had the lowest radiation yield and the lowest stability, was observed as a species of four resonance lines. The two inner constituents of these four lines were partially obscured by the two central doublets originating from species I and II. The latter were relatively stable and had activation energies around 35 kJ/mol. The percentage concentrations of the involved species were estimated by comparing experimental and calculated spectra. The reasonably high radical yields of the dl-TA in the dose range of interest, the fairly good stabilities of the species produced (I and II) at room temperature, and the almost linear features of the constructed dose-response curves led us to conclude that the intensities associated with the stable species (I and II) could be used to estimate the applied dose in the dose range of 100 Gy-34 kGy with fairly good accuracy and that dl-TA could be a good candidate for exploring low radiation dose measurements by ESR dosimetry.

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Many efforts have been made to develop neutron capture therapy (NCT) for cancer treatment. Among the challenges in using NCT is the characterization of the features of the mixed radiation field and of its components. In this study, we examined the enhancement of the ESR response of pellets of alanine and ammonium tartrate with gadolinium oxide exposed to a thermal neutron beam. In particular, the ESR response of these dosimeters as a function of the gadolinium content inside the dosimeter was analyzed. We found that the addition of gadolinium improves the sensitivity of both alanine and ammonium tartrate. However, the use of gadolinium reduces or abolishes tissue equivalence because of its high atomic number (Z(Gd) = 64). Therefore, it is necessary to find the optimum compromise between the sensitivity to thermal neutrons and the reduction of tissue equivalence. Our analysis showed that a low concentration of gadolinium oxide (of the order of 5% of the total mass of the dosimeter) can enhance the thermal neutron sensitivity more than 13 times with an insignificant reduction of tissue equivalence.

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In this paper we present an investigation of the electron spin resonance (ESR) line shape of ammonium tartrate (AT) dosimeters exposed to radiation with different linear energy transfer (LET). We exposed our dosimeters to gamma-ray photons ((60)Co), 7 MeV and 14 MeV initial energy electrons, and 19.3 MeV initial energy protons. The differences in the power saturation behavior of ESR spectra of AT irradiated with photons, electrons and protons could be correlated to the effective LET of the radiation beams. We analyzed the behavior of peak-to-peak amplitude as a function of microwave power, and we developed a fitting procedure that permits us to obtain the dependence of the homogeneity parameter of the line shape on the LET of the radiation using the Castner saturation theory. This simple procedure allows us to distinguish the LET of the radiation beam.

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Solid state pellets (1 mm thick) for electron spin resonance (ESR) dosimetry were made using ammonium tartrate as the radiation-sensitive substance. Their behaviour was experimentally investigated as a function of dose with 60Co gamma rays. The calibration function obtained permits measurements of absorbed dose in the 2-50 Gy range, with a combined uncertainty of +/-4%. The lowest detectable dose was about 0.5 Gy. These properties are comparable with or even better than those of ESR dosimeters made from other materials. The time stability of the ESR signal of ammonium tartrate dosimeters at different storage conditions after irradiation was studied. A rather complex behaviour was observed, which suggests that more species of free radicals are produced by radiation and that migration processes may be effective. No dependence of the response on beam quality was found for high-energy photon and electron beams produced by a linear accelerator used in radiotherapy, whereas dose was underestimated with low-energy x-rays.

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The crystalline substance ammonium tartrate is investigated with respect to its suitability as a clinical dosimetry material. The properties investigated are: the radical stability for absorbed doses relevant for clinical use, the improvement in sensitivity when the crystals are deuterated and the linear electron transfer (LET)-dependence. After photon irradiation to an absorbed dose of 20 Gy, the signal increases rapidly during the first 6 h. After this period, the changes are more moderate and can be corrected for. The signal-to-noise ratio of irradiated ammonium tartrate is twice the corresponding value of alanine. By deuterating the crystals, the sensitivity can be further improved by a factor of 1.4. As expected, the signal decreases with increasing LET of the radiation, but no changes in the spectrum shape was observed.

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Several single crystals and powder samples of ammonium tartrate, recently proposed as a possible ESR dosimeter, have been X-irradiated with different doses. The total radical concentration has been determined by quantitative cw ESR, by comparison with a standard. The samples have been studied by electron spin echo spectroscopy. The two-pulse echo decay has been obtained and simulated by a single exponential function for different values of the microwave power of the pulses and for different pulse lengths. The dependence of the phase memory time TM on the microwave power has been exploited to get information on the contribution of the instantaneous diffusion to spin dephasing. At room temperature in the range of radical concentrations of 10(18)-10(19) spins/cm3 the instantaneous diffusion is the dominant spin dephasing mechanism. The linear dependence of the instantaneous diffusion on the total concentration of the radicals is in agreement with the theory. From the latter result we conclude that the average radical-radical distance corresponds to a random distribution of the radicals in the matrix. A simple method of measuring the radical concentration by the ESE decays in powder samples of irradiated ammonium tartrate is described.

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New results and discussions since 1977 are reviewed. It is stated that--excepting Kovács's crystallization experiments not yet repeated in independent laboratories--positive, unconfuted results do not exist. Considering also the results of the different amplification theories it seems to be very improbable that the weak interaction played any role in establishing the nearly complete asymmetry of biomolecules.

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A novel approach has been introduced to detect the manifestation of symmetry breaking weak interactions at molecular level. In the racemic conglomerate crystallization of D,L-sodium-ammonium tartrate the effect of 32P irradiation was studied by measuring the weight and optical purity of the crystalline phase as well as the size distribution of the crystallites. The high number of independent experiments (over 1000) permitted statistical analysis of the results. The following observations have been made: 1. Beta irradiation influences the crystallization process, irradiated samples yield more crystalline material. 2. The effect involves presumably crystal seed formation because from the irradiated solutions more and smaller crystallites are formed. 3. The presence of beta particles induces stereoselective crystallization, the crystalline phase shows optical activity characteristic of the "unnatural" L-isomer. 4. The above changes are attributed to the beta irradiation as the magnitude of the effects depends on the amount of added radioactivity. Optically active contaminants are highly unlikely sources of the differences between irradiated and control series. 5. In the absence of 32P the tartrate enantiomers have equal probability to form crystals, i.e., the contribution of mixing of weak interaction into the electromagnetic one is not measurable in this system.

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In the racemic conglomerate crystallization of over 1,000 samples of D,L-sodium-ammonium tartrate the effect of 32P beta irradiation on the weight, optical activity, and crystallite size was measured. Both weight and optical activity showed a statistical dependence on the intensity of beta irradiation. The crystallite size is also affected by the presence of 32P. Asymmetric crystals are suggested to have been potential mediators between asymmetric parity violating forces and molecular asymmetry so that stereo-selective prebiotic chemical reactions involving crystals need not be considered 'chance' processes. No measurable difference in the energy content of optical isomers was found. An upper limit for the direct contribution of weak interactions to electromagnetic ones has been calculated. The mechanism of stereoselective crystal seeding by beta particles is discussed.

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